Optical Circulator For Free Space Optical Communication

ABSTRACT

A free space optical communication system transmits and receives optical signals in a colorless manner using an optical circulator. The system installs the optical circulator with a single mode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and a multimode (MM) fiber at port 3. The system injects a first optical signal into a core of the SM fiber. The system then routes the first optical signal at port 1, using the optical circulator, into a SM core of the DC fiber via Port 2. Further, the system injects a second optical signal into a first cladding of the DC fiber. The system then routes the second optical signal at port 2, using the optical circulator, into the MM fiber via Port 3.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/290,153, filed Oct. 11, 2016, the disclosure of which isincorporated herein by reference.

BACKGROUND

Free space optical communications (FSOC) links are used to transmitinformation through free space between terminals. Optical transmittersand receivers are aligned to establish line of sight connections for thedata to be transmitted and received. Often, fiber optic components, suchas fiber optic amplifiers, are used. Hence, optical alignment has to beestablished between two optical fiber tips that are separated by, forexample, a significant distance. In such a FSOC system, transmitting theoptical beam from a single mode (SM) fiber may be required, so that theoptical signal can propagate in Gaussian beam to ensure the focusabilityat the far end. A high degree of pointing accuracy may be required toensure that the optical beam will be received.

SUMMARY

A method and system are provided for transmitting an optical signal in aSM fiber and receiving the optical signal in a multimode (MM) fiber in acolorless manner. An optical beam may be received into the MM fiber,having a larger diameter than the SM fiber, so that the pointingaccuracy can be relaxed while the line of sight is still established.Furthermore, the transmitting and receiving optics are colorless.Accordingly, the transmitting and receiving wavelength(s) do not need tobe predetermined. In this regard, the network has the flexibility toreconfigure the wavelength assignments, and optics need not be alignedin the free space.

A system may comprise an optical circulator having a first port, asecond port, and a third port. A first fiber is coupled to the firstport of the optical circulator, a second fiber is coupled to the secondport of the optical circulator, and a third fiber is coupled to thethird port of the optical circulator. The optical circulator is adaptedto route optical signals between at least two of the coupled fibers. Forexample, the first fiber may be a SM fiber, the second fiber may be a DCfiber, and the third fiber may be a MM fiber. The optical circulator maybe adapted to route optical signals from the SM fiber to the DC fiber,and may be further adapted to route optical signals from the DC fiber tothe MM fiber. The DC fiber may be configured to transmit and receiveoptical signals through free space, and may be coupled to a collimatorused for receiving the optical signals. In some examples, one or moretransmitters are coupled to the SM fiber, and one or more receiverscoupled to the MM fiber, wherein the system is configured to transmitoptical signals using a first channel, and to simultaneously receiveoptical signals using a second channel. The one or more transmitters maycomprise a tunable transmitter, or they may be input to a single modewavelength division multiplexer. A tunable filter may be coupled betweenthe MM fiber and the one or more receivers. The one or more receiversmay comprise multiple receivers coupled to the MM fiber through amultimode wavelength division multiplexer. The system may be wavelengthinsensitive, and wavelengths need to be predetermined for communicationwith other FSOC systems.

Another aspect of the disclosure provides a platform, comprising one ormore FSOC systems, each FSOC system comprising an optical circulatorhaving a first port, a second port, and a third port, wherein theoptical circulator is wavelength insensitive, a single mode fibercoupled to the first port of the optical circulator, a double clad fibercoupled to the second port of the optical circulator, and a multimodefiber coupled to the third port of the optical circulator, wherein theoptical circulator is adapted to route optical signals from the singlemode fiber to the double clad fiber, and wherein the optical circulatoris further adapted to route optical signals from the double clad fiberto the multimode fiber. The platform may be, for example, a mobileplatform. The platform may further comprise a control unit incommunication with a control system, which may be adapted to adjust aposition of the platform and/or provide instructions identifying whichchannel to use for transmission of optical signal and which channel touse for receipt of optical signals.

One aspect of the disclosure provides a method of optical communicationby a first terminal, comprising injecting a first optical signal into acore of a single mode fiber coupled to a first port of an opticalcirculator, routing, using the optical circulator, the first opticalsignal into a core of a double clad fiber, the double clad fiber beingcoupled to a second port of the optical circulator, and transmitting thefirst optical signal through free space to a second terminal. In someexamples, the method further comprises injecting a second optical signalinto a first cladding of the double clad fiber, and routing, using theoptical circulator, the second optical signal into a multimode fiber ata third port of the optical circulator. The first optical signal may beamplified prior to routing the first optical signal to the double cladfiber. For example, a single mode wavelength division multiplexer mayamplify two bands of optical signals input thereto. Transmitting thefirst optical signal through free space may include transmitting thefirst optical signal on a first channel, and in this regard the methodmay further include receiving, by the double clad fiber, a secondoptical signal through free space from the second terminal on a secondchannel simultaneously with the transmitting. Further, a bi-directionaloptical link with the second terminal may be maintained, such that byswitching channels, a third optical signal can be transmitted on thesecond channel and a fourth optical signal can be received on the firstchannel, without breaking the bi-directional optical link.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 illustrates an example fiber pigtailed optical circulator used inan FSOC system according to aspects of the disclosure.

FIG. 2 illustrates an example operation of the fiber pigtailed opticalcirculator system of FIG. 1.

FIG. 3 illustrates an example communication between two FSOC systemsaccording to aspects of the disclosure.

FIG. 4 illustrates another example communication between two FSOCsystems according to aspects of the disclosure.

FIG. 5 is a block diagram of an example platform including the fiberpigtailed optical circulator system of FIG. 1.

FIG. 6 is a flow diagram illustrating an example method according toaspects of the disclosure.

FIG. 7 is a pictorial diagram illustrating an example communicationbetween two platforms including FSOC systems according to aspects of thedisclosure.

FIG. 8 is another example of communications among platforms and otherentities according to aspects of the disclosure.

FIG. 9 is an example diagram illustrating communication among platformsincluding multiple FSOC systems according to aspects of the disclosure.

DETAILED DESCRIPTION

The systems and techniques described herein relate to a FSOC systemhaving an optical circulator installed within a SM fiber, a double clad(DC) fiber, and a MM fiber. The system can be implemented for use in anyof a variety of environments. For example, the system can be implementedlocally on a client device or implemented across a client device andserver environment. The client device can be any communication devicesuch as an optical communication device, optical transmitters, opticalreceivers, or FSOC base stations, etc. In one particular example, thesystem may be implemented in a high-altitude platform, such as anaircraft, an unmanned aerial vehicle (UAV), a balloon, a satellite,etc., and may be used to communicate with other high-altitude platformsor grounded devices.

FIG. 1 illustrates an example fiber coupled optical circulator system100, including a SM fiber 110, a MM fiber 120, and a DC fiber 130 eachin communication with an optical circulator 140. For example, each ofthe SM fiber 110, MM fiber 120, and DC fiber 130 can be fiber pigtailedwith the optical circulator 140. In fiber optics, an optical signal isguided down the center of a fiber called the core. The core issurrounded by a cladding, which is an optical material that traps thelight in the core using at least one of an optical technique. Forexample, the cladding may trap the light via total internal reflection.

The SM fiber 110 includes a core 114 and cladding 112. The SM fiber 110is designed to support one transverse mode, carrying light parallel to alength of the fiber. The light may have different frequencies. A corediameter of the SM fiber may be relatively small, for example between 8and 10.5 μm, with a cladding diameter of approximately 125 μm. It shouldbe understood that these dimensions are merely examples, and that otherdimensions may be used. In some examples, the SM fiber may be chemicallyor physically altered to have special properties.

The MM fiber 120 includes a core 124 and cladding 126. The MM fiber 120has a larger core diameter than the SM fiber 110. By way of exampleonly, the core diameter of the MM fiber 120 may be approximately 50-100μm. Accordingly, the MM fiber 120 may support more than one propagationmode.

The DC fiber 130 may include multiple layers of optical material, suchas a core, an inner cladding, and an outer cladding. For example, the DCfiber 130 has the SM core 134 that is surrounded by a first cladding 132to support the SM optical guiding. The first cladding 132 is surroundedby a second cladding 136. In this example, the first cladding 132 itselfis a MM optical waveguide, which may match with the MM fiber 120 for lowcoupling loss.

The optical circulator 140 is a fiber optic component that can be usedto direct optical signals. The circulator 140 may have multiple portsfor coupling to multiple fibers. For example, as shown in FIG. 1, theoptical circulator 140 is pigtailed with the fibers 110-130, such thatthe SM fiber 110 is coupled to a first port, the DC fiber 130 is coupledto a second port, and the MM fiber 120 is coupled to a third port.Accordingly, optical signals received at a fiber at one port may bedirected to another fiber at another port.

The example arrangement of fibers and ports described above and hereinmay be varied. For example, the SM fiber 110, MM fiber 120, and DC fiber130 may be fiber coupled to different ports of the optical circulator140. As a further example, different types of fibers may be used.

FIG. 2 provides an example of how to use the fiber pigtailed circulator100 in an FSOC system. A first optical signal 205 is injected into thecore of the SM fiber 110. The first optical signal 205 from port 1 isrouted by the optical circulator 140 to the SM core of port 2, whichthen exits the optical circulator as a transmitting signal 215. Thefirst optical signal may thus be transmitted to a second FSOC system(not shown).

A second optical signal 225 is received, for example from the secondFSOC system, into the first cladding of the DC fiber 130 which acts as aMM waveguide. The second optical signal 225 from port 2 is then routedto port 3 which is pigtailed with the MM fiber 120.

The FSOC system of FIG. 2 is not wavelength selective. Accordingly, intransmitting and receiving optical signals between the FSOC system ofFIG. 2 and another FSOC system, a wavelength of the transmitted orreceived signals does not need to be predetermined. Rather, anywavelength may be sent or received.

FIG. 3 illustrates how an optical circulator is used in the FSOC systemto transmit an optical signal from a SM fiber 320 and to receive theoptical signal into a MM fiber. A system architecture has two terminals,a west terminal 350 and an east terminal 360. Each terminal has atransmitter (TX_(West) and TX_(East), respectively) and each transmittermay include one or multiple optical channels, illustrated as bands TX B1and TX B2. A SM wavelength division multiplexer (WDM) 315 at TX_(West)combines these two channels or bands of optical signals into an optionaloptical amplifier 370. The output of the amplifier is connected to port1 of the optical circulator and is routed to the SM core of a DC fiber340 of Port 2. In this example, west terminal 350 transmits on a firstchannel.

The optical signal is then propagated in the free space to the eastterminal 360 and received into the first cladding of a DC fiber 345which is a MM optical waveguide. In some examples, focusing optics, suchas a collimator 385, may be used in receiving the optical signal at theeast terminal 360. For example the collimator 385 may help to narrow abeam of the received signal prior to receipt by the DC fiber 245, suchthat the DC fiber 345 receives a narrower beam (e.g., having a betteralignment of rays or a narrower cross section). Afocal telescopes may beused conjunction with the fiber pigtailed collimators to expand theoptical beam for providing optical antenna gain, so that the opticalloss between the transmitter and the receiver is reduced. Beam pointing,tracking and acquisition schemes may also be used to establish the lineof sight connection between these two terminals. This received signal isthen routed to the Port 3 MM fiber 330 of the circulator and is receivedby the receiver. With this arrangement, transmitting from SM fiber 320and receiving into MM fiber 330 is realized.

Just as the west terminal 350 can transmit on one or more channels, theeast terminal 360 can receive on one or more channels. Depending on thelink loss between the east and west terminals, the transmitting powercould be much higher than the receiving power. As a result, if there isany leakage or crosstalk from the transmitter to the receiver throughthe circulator and the collimator of the same terminal, the receivingsignal is contaminated by this crosstalk. To resolve this issue, Port 3of the circulator is followed by a MM WDM 390 to separate the wavelengthbands of the two channels. In some examples, the MMWDM 390 may be adense WDM (DWDM), or it may be followed by a DWDM to separate thereceiving channels into multiple fibers if there are multipletransmitting wavelengths in the transmitting channel MM bandpass filters392, 394 can be placed between the MM WDM 390 and receivers 362, 364.When a terminal is transmitting in a certain wavelength band, thereceiver assigned with the same wavelength band can be set in the idlemode electronically and only the receiver assigned with the oppositewavelength band is used to receive the signals from the far endterminal. Thus, in this example the west terminal transmits on the firstchannel and the east terminal receives on the first channel, while theeast terminal 360 transmits on a second channel and the west terminalreceives on the second channel. However, in other examples the channelsmay be varied. Further, in other example systems more than two channelsmay be available.

Because the circulator is wavelength insensitive, the whole architectureis colorless in the sense that the east terminal 360 and the westterminal 350 can switch the transmitting and the receiving wavelengthswithout breaking the bidirectional optical link. Other wavelengthmanagement devices, such as wavelength division multiplexers and/ordemultiplexers, as well as optical filters may be used to enhance theoptical signal integrity or to increase the flexibility of the opticalchannel planning.

FIG. 4 illustrates an alternative architecture of FIG. 3. As illustratedin FIG. 4, an optional MM optical preamp 450 is used to increase thereceiving sensitivity. Because the receiving path is in MM fibers 410via the first clad of the DC fiber 420 and the MM fiber 410 of the Port3 of the circulator 440, the preamp in the receiving path is illustratedas a MM optical preamp 450. Also as in FIG. 4, a tunable transmitter 430can be used in both terminals. A tunable transmitter 430 can include onewavelength or multiple independently modulated laser wavelengths.Furthermore, a MM tunable bandpass filter 460 can be used to selectcertain wavelength band(s). The receiver (RX) may be a single photodiodeor multiple spectrally separated photodiodes.

FIG. 5 illustrates an example method 500 for transmitting and receivingan optical signal using an optical circulator in a colorless mannerMethod 500 can be performed by, for example, the FSOC system of thepresent disclosure.

In block 510, the system installs an optical circulator with a singlemode (SM) fiber at port 1, a double clad (DC) fiber at port 2, and amultimode (MM) fiber at port 3. This arrangement of the fibers is merelyan example, and other arrangements of the fibers in relation to theports of the optical circulator are possible.

In block 520, the system injects a first optical signal into a core ofthe SM fiber. The first optical signal may be generated by, for example,a transmitter in response to commands from one or more processors. Insome examples, the first optical signal may be amplified prior toinjection into the SM fiber.

In block 530, the system routes the first optical signal at port 1,using the optical circulator, into a SM core of the DC fiber via Port 2.

In block 540, the system injects a second optical signal into a firstcladding of the DC fiber. The second optical signal may be receivedfrom, for example, a second FSOC system.

In block 550, the system routes the second optical signal at port 2,using the optical circulator, into the MM fiber via Port 3. Hence, thesecond optical signal acts as a received signal in the MM fiber. Theoptical circulator is not wavelength sensitive, as a result, andpromotes colorless transmitting from an SM fiber and receiving into anMM fiber.

As mentioned above, the FSOC system may be used in connection with oneor more computing devices on a platform. The platform may be a groundedplatform, such as a controller, base station, or any other computingdevice. The platform may alternatively be a mobile platform, such as acar, buoy, laptop computer, etc. In further examples, the platform maybe a high-altitude platform, such as a drone, satellite, balloon, or thelike.

FIG. 6 is a block diagram illustrating an example platform 605,including various components. The platform may have one or morecomputers, such as computer 610 containing a processor 620, memory 630and other components typically present in general purpose computers. Theone or more computers may be in communication with a FSOC system 600,which includes an optical circulator coupled to a SM fiber, MM fiber,and DC fiber as described in the examples above.

The memory 630 stores information accessible by processor 620, includinginstructions 632 and data 634 that may be executed or otherwise used bythe processor 620. The memory 630 may be of any type capable of storinginformation accessible by the processor, including a computer-readablemedium, or other medium that stores data that may be read with the aidof an electronic device, such as a hard-drive, memory card, ROM, RAM,DVD or other optical disks, as well as other write-capable and read-onlymemories. Systems and methods may include different combinations of theforegoing, whereby different portions of the instructions and data arestored on different types of media.

The instructions 632 may be any set of instructions to be executeddirectly (such as machine code) or indirectly (such as scripts) by theprocessor. For example, the instructions may be stored as computer codeon the computer-readable medium. In that regard, the terms“instructions” and “programs” may be used interchangeably herein. Theinstructions may be stored in object code format for direct processingby the processor, or in any other computer language including scripts orcollections of independent source code modules that are interpreted ondemand or compiled in advance. Functions, methods and routines of theinstructions are explained in more detail below.

The data 634 may be retrieved, stored or modified by processor 620 inaccordance with the instructions 632. For instance, although the systemand method is not limited by any particular data structure, the data maybe stored in computer registers, in a relational database as a tablehaving a plurality of different fields and records, XML documents orflat files. The data may also be formatted in any computer-readableformat. The data may comprise any information, such as numbers,descriptive text, proprietary codes, references to data stored in otherareas of the same memory or different memories (including other networklocations) or information that is used by a function to calculate therelevant data.

The processor 620 may be any conventional processor, such as processorsfrom Intel Corporation or Advanced Micro Devices. Alternatively, theprocessor may be a dedicated device such as an ASIC. Although FIG. 6functionally illustrates the processor, memory, and other elements ofcomputer 610 as being within the same block, it will be understood bythose of ordinary skill in the art that the processor and memory mayactually comprise multiple processors and memories that may or may notbe stored within the same physical housing. For example, memory may be ahard drive or other storage media located in a server farm of a datacenter. Accordingly, references to a processor or computer will beunderstood to include references to a collection of processors orcomputers or memories that may or may not operate in parallel.

Computer 610 may include all of the components normally used inconnection with a computer such as a central processing unit (CPU),graphics processing unit (GPU), memory (e.g., RAM and internal harddrives) storing data 634 and instructions such as a web browser, anelectronic display (e.g., a monitor having a screen, a small LCDtouch-screen or any other electrical device that is operable to displayinformation), and user input (e.g., a keyboard, touchscreen and/ormicrophone).

Computer 610 may also include a geographic position component 644 todetermine the geographic location of the platform 605. For example,computer 610 may include a GPS receiver to determine the platform'slatitude, longitude and/or altitude position. Other location systemssuch as laser-based localization systems, inertial-aided GPS, orcamera-based localization may also be used.

Computer 610 may also include other features, such as an accelerometer,gyroscope or other acceleration device 646 to determine the direction inwhich the device is oriented. By way of example only, the accelerationdevice may determine its pitch, yaw or roll (or changes thereto)relative to the direction of gravity or a plane perpendicular thereto.In that regard, it will be understood that a computer's provision oflocation and orientation data as set forth herein may be providedautomatically to the user, other computers of the network, or both.

Computer 610 may also include an object detection component 648 todetect and identify objects, such as other platforms, birds, powerlines, utility poles, or other obstructions. The detection system mayinclude lasers, sonar, radar, cameras or any other such detectionmethods. In use, computer 610 may use this information to instruct thenavigation system 370 to update a position of the platform 605.

Computer 610 may send and receive information from the various systemsof platform 605, for example the navigation 670 system in order tocontrol the movement, speed, etc. of platform 605. In some examples,such information may be received at the computer from another entity,such as a wireless ground controller. For example, computer 610 may becapable of communicating with a remote server or other computer (notshown) configured similarly to computer 610, with a processor, memory,instructions, and data. The remote server or other computer may receiveposition information and/or other information from the sensors 680and/or FSOC system 600. In other examples, such information may bedetermined by the computer 610 based on information detected by sensors680 or other components of the platform 605.

It will be understood that although various systems and computer 610 areshown within platform 605, these elements may be external to platform605 or physically separated.

FIG. 7 illustrates an example network including communication betweenand among two platforms and one or more ground terminals. As shown, afirst platform 710 includes FSOC system 715, and a second platform 720includes FSOC system 725. Each of the FSOC systems 715, 725 may includean optical circulator coupled to optical fibers as described in theexamples above. In this regard, the FSOC systems 715, 725 may transmitand receive optical signals therebetween, and thus send data and otherinformation between the platforms 710, 720.

As further illustrated in FIG. 7, one or more ground terminals may alsocommunicate directly with the platforms 710, 720, either through theFSOC systems 715, 725 or through other communication devices on theplatforms 710, 720. For example, ground terminals 762, 764 may bepositioned at ground level, on top of buildings, or the like. The groundterminals 762, 764 may communicate with the platforms 710, 720,respectively, through gateway uplinks (GW-UL) and gateway downlinks(GW-DL). In other examples, the ground terminals may include opticalsystems capable of optical communication with the FSOC systems 715, 725.Similarly, mobile devices such as tablet 772 and smartphone 774 may alsodirectly communicate with the platforms 710, 720, through direct-to-user(DTU) uplinks or downlinks or optical signals.

FIG. 8 is another example of communications among platforms and otherentities. In addition to each platform 810, 820 including a FSOC system,each platform 810, 820 may further include a control-and-non-payloadcommunication (CNPC) unit, such as CNPC units 819, 829. The CNPC units819, 829 may include transceivers capable of wireless communication withCNPC ground terminal 860. For example, the CNPC units 819, 829 andground terminal 960 may communicate via radio. The CNPC ground terminal860 may further communicate with a network configuration and pointingsystem 880, for example, via a wired link. In this regard, the networkconfiguration and pointing system 860 may provide information to theplatforms 810, 820 through the CNPC ground terminal 860. Suchinformation may include, by way of example only, positioninginformation. Such positioning information may be used to adjust analignment of components in the FSOC system, such that optical signalssent by one platform are accurately received by the other. According toother examples, such information provided through the CNPC may includeinstructions regarding which channels to use for transmission of opticalsignals and which channels to use for receipt of optical signals.

FIG. 9 is an example diagram illustrating communication among platformsincluding multiple FSOC systems. For example, platform 910 includesthree FSOC systems 913, 915, 917. Each of these FSOC systems 913, 915,917 may communicate with another FSOC system on another platform. Forexample, as shown, the FSOC system 813 communicates with FSOC system 843on platform 940, FSOC system 915 communicates with FSOC system 937 onplatform 930, and FSOC system 917 communicated with FSOC system 925 onplatform 920. Accordingly, one platform may conduct opticalcommunications with multiple other platforms simultaneously.

The techniques described above may also be used in a Lidar system. Forexample, the first optical signal may be the transmitted signal,consisting of optical pulses, and the second optical signal is thereflected signal from an object of interest.

The subject matter described herein can be implemented in softwareand/or hardware (for example, computers, circuits, or processors). Thesubject matter can be implemented on a single device or across multipledevices (for example, a client device and a server device). Devicesimplementing the subject matter can be connected through a wired and/orwireless network. Specific examples disclosed are provided forillustrative purposes and do not limit the scope of the disclosure.

Moreover, an arrangement of fibers or types of fibers used with theoptical circulator may be varied.

Unless otherwise stated, the foregoing alternative examples are notmutually exclusive, but may be implemented in various combinations toachieve unique advantages. As these and other variations andcombinations of the features discussed above can be utilized withoutdeparting from the subject matter defined by the claims, the foregoingdescription of the embodiments should be taken by way of illustrationrather than by way of limitation of the subject matter defined by theclaims. In addition, the provision of the examples described herein, aswell as clauses phrased as “such as,” “including” and the like, shouldnot be interpreted as limiting the subject matter of the claims to thespecific examples; rather, the examples are intended to illustrate onlyone of many possible embodiments. Further, the same reference numbers indifferent drawings can identify the same or similar elements.

1. A system, comprising: an optical circulator having a first port, asecond port, and a third port; a single mode fiber coupled to the firstport of the optical circulator; a double clad fiber coupled to thesecond port of the optical circulator; and a multimode fiber coupled tothe third port of the optical circulator; a transmitter coupled to thesingle mode fiber, the transmitter transmitting first optical signalsusing a first channel, wherein the transmitter comprises a tunabletransmitter; a receiver coupled to the multimode fiber, the receiverreceiving second optical signals using a second channel simultaneouslywith the transmitting by the transmitters; and a multimode tunablefilter coupled between the multimode fiber and the receiver; wherein theoptical circulator routes the first or second optical signals among thesingle mode, double clad, and multimode fibers.
 2. The system of claim1, wherein the optical circulator is adapted to route optical signalsfrom the single mode fiber to the double clad fiber, and wherein theoptical circulator is further adapted to route optical signals from thedouble clad fiber to the multimode fiber.
 3. The system of claim 1,wherein the system is wavelength insensitive.
 4. The system of claim 1,further comprising a collimator coupled to the double clad fiber,wherein the double clad fiber is configured to transmit the opticalsignals through free space, and to receive optical signals through freespace.
 5. A platform, comprising: one or more free space opticalcommunication (FSOC) systems, each FSOC system comprising: an opticalcirculator having a first port, a second port, and a third port; asingle mode fiber coupled to the first port of the optical circulator; adouble clad fiber coupled to the second port of the optical circulator;and a multimode fiber coupled to the third port of the opticalcirculator; a transmitter coupled to the single mode fiber, thetransmitter transmitting first optical signals using a first channel,wherein the transmitter comprises a tunable transmitter; a receivercoupled to the multimode fiber, the receiver receiving second opticalsignals using a second channel simultaneously with the transmitting bythe transmitters; and a multimode tunable filter coupled between themultimode fiber and the receiver; wherein the optical circulator isadapted to route at least one of the first or second optical signalsfrom the single mode fiber to the double clad fiber, and wherein theoptical circulator is further adapted to route at least one of the firstor second optical signals from the double clad fiber to the multimodefiber; and a computing device in communication with the one or more FSOCsystems, the computing device including one or more processorsconfigured to control at least one of operation of the one or more FSOCsystems or movement of the platform.
 6. The platform of claim 5, furthercomprising a navigation system configured to control movement of theplatform.
 7. The platform of claim 5, further comprising a control unitin communication with the computing device, the control unit configuredto adjust a position of the platform.
 8. The platform of claim 5,further comprising a control unit in communication with the computingdevice, the control unit configured to provide instructions identifyingwhich channel to use for transmission of optical signals and whichchannel to use for receipt of optical signals.
 9. The platform of claim5, wherein each FSOC system is wavelength insensitive.
 10. A method ofoptical communication, comprising: injecting a first optical signal intoa core of a single mode fiber coupled to a first port of an opticalcirculator; routing, using the optical circulator, the first opticalsignal into a core of a double clad fiber, the double clad fiber beingcoupled to a second port of the optical circulator; transmitting, usinga tunable transmitter, the first optical signal through free space on afirst channel; and receiving, by the double clad fiber, a second opticalsignal through free space from a terminal on a second channelsimultaneously with the transmitting.
 11. The method of claim 10,further comprising: injecting a third optical signal into a firstcladding of the double clad fiber; and routing, using the opticalcirculator, the third optical signal into a multimode fiber at a thirdport of the optical circulator.
 12. The method of claim 10, furthercomprising amplifying the first optical signal prior to routing thefirst optical signal to the double clad fiber.
 13. The method of claim12, further comprising combining, using a single mode wavelengthdivision multiplexer, two bands of optical signals input to anamplifier.
 14. The method of claim 10, wherein transmitting the firstoptical signal through free space comprises transmitting the firstoptical signal on a first channel, and further comprising receiving, bythe double clad fiber, a second optical signal through free space from aterminal on a second channel simultaneously with the transmitting. 15.The method of claim 10, further comprising: maintaining a bi-directionaloptical link with the terminal; and switching channels to transmit athird optical signal on the second channel and receive a fourth opticalsignal on the first channel, without breaking the bi-directional opticallink.